Describe the proper handling of a fluoride/oxalate (gray-top) tube used for glucose testing.

• A. Shake vigorously after collection
• B. Store at room temperature for 24 hours before processing
• C. Let the tube sit upright for 2 hours before inversion
• D. Invert 8–10 times to mix; transport and process promptly; glycolysis inhibitor preserves glucose.

Answer: (D)

For glucose testing with a fluoride/oxalate gray-top tube, the goal is to prevent glycolysis and keep the glucose concentration accurate. The tube contains sodium fluoride, a glycolysis inhibitor, and potassium oxalate, an anticoagulant. To ensure proper distribution of these additives and to prevent clotting, invert the tube 8–10 times immediately after collection. Then transport and process promptly, so the sample is analyzed before glycolysis can lower the glucose level. The fluoride helps preserve glucose, but its effect is only reliable if the sample is processed quickly; delaying processing or leaving the sample at room temperature for extended periods allows glycolysis to continue, giving falsely low results. Shaking vigorously is not advised, as it can cause hemolysis and other issues.